1. Field of the Invention
The present invention relates to a pouch-type lithium secondary battery and a method of manufacturing the same. More particularly, the invention is directed to a pouch-type lithium secondary battery using a part of the pouch material to perform packing processes, so that an additional packing case is not needed, thereby simplifying the packing processes.
2. Discussion of Related Art
Recently, compact and light electrical and electronic apparatuses such as mobile telephones, notebook computers, and camcorders have been actively developed and produced. Battery packs are built-in to these portable electrical and electronic apparatuses, enabling the apparatuses to operate when other power sources are not available. The built-in battery packs each include at least one battery for outputting a uniform level voltage to drive the portable electrical and electronic apparatus for a desired period of time.
For economical reasons, secondary batteries (which can be charged and discharged) have recently been used as the battery packs. Secondary batteries include lithium secondary batteries such as lithium (Li) batteries and lithium ion (Li-ion) batteries, as well as nickel-cadmium (Ni—Cd) batteries and nickel-hydrogen (Ni-MH) batteries.
In particular, since lithium secondary batteries commonly operate at a voltage of 3.6 V (which is three times greater than the operation voltages of the Ni—Cd batteries and Ni—H batteries that are widely used as power sources for portable electronic apparatuses), and since the energy density per unit weight of lithium ion secondary batteries is high, the use of lithium ion secondary batteries has rapidly increased.
In lithium secondary batteries, lithium-based oxides are used as the positive electrode active materials, and carbon materials are used as the negative electrode active materials. In general, lithium ion secondary batteries are divided into liquid electrolyte batteries and polymer electrolyte batteries according to the kind of electrolyte used. Batteries using liquid electrolytes are referred to as lithium ion batteries, and batteries using polymer electrolytes are referred to as lithium polymer batteries. Also, lithium secondary batteries are manufactured in various shapes, such as cylinders, polygons, and pouches.
In general, in pouch-type lithium secondary batteries, the pouch material is commonly formed of multiple layers of metal foil and a synthetic resin layer which cover the metal foil layers. When pouch-type lithium secondary batteries are used, the weight of the battery (in comparison with cylinder- and polygon-type lithium secondary batteries in which metal cans are used) can be significantly reduced. Therefore, in order to reduce the weight of lithium secondary batteries, pouch-type lithium secondary batteries have been developed.
In general, in pouch-type lithium secondary batteries, an electrode assembly is placed on the bottom surface of the pouch material (which includes a space for accommodating the electrode assembly). The bottom surface is then covered with the top surface of the pouch material and the pouch is sealed to form a pouch bare cell. Accessories, such as protective circuit modules, are attached to the pouch bare cell to form a pouch core pack and the pouch core pack is built-in to an additional battery packing case.
However, when the additional battery packing case of the pouch-type lithium secondary battery is used as described above, processes are complicated, and there are limitations on the improvement of the productivity per unit time of the pouch-type lithium secondary battery. Also, since an additional battery packing case is used, reductions in the manufacturing cost of the pouch-type lithium secondary battery are limited.